The present invention relates generally to the field of magnetic data storage and retrieval systems. In particular, the present invention relates to a thin film transducing head having improved performance due to reduced thermal pole tip protrusion and recession.
In a magnetic data storage and retrieval system, a thin-film transducing head typically includes a transducer, a substrate upon which the transducer is built, and an overcoat deposited over the transducer. The transducing head often times includes a basecoat, which forms an interface layer between the substrate and the transducer and is generally formed of an insulating material. The transducer, which typically includes a writer portion for recording and storing magnetically-encoded information on a magnetic media and a reader portion for retrieving that magnetically-encoded information from the magnetic media, is formed of multiple patterned layers successively stacked upon the basecoat. The volume of the transducer is typically much smaller than both the volume of the substrate and the volume of the overcoat.
The layers of the transducer, which include both metallic and insulating layers, all have differing mechanical and chemical properties than the substrate. These differences in properties affect several aspects of the transducer. First, the layers of the transducing head will be lapped at different rates. Thus, when an air bearing surface (ABS) of the transducing head is lapped during its fabrication, differing amounts of the layers will be removed, resulting in the transducing head having an uneven ABS. Commonly, a greater amount of the metallic layers of the transducer will be removed during the lapping process than will be removed from the substrate. Thus, the lapping process results in a pole tip recession (PTR) of the metallic layers of the transducer with respect to the substrate. The PTR of a particular layer is defined as the distance between the air bearing surface of the substrate and the air bearing surface of that layer.
The differing mechanical and chemical properties of the substrate and transducer layers affect the air bearing surface during operation of the transducing head. As the magnetic data storage and retrieval system is operated, the transducing head is subjected to increased temperatures within the magnetic data storage and retrieval system. In addition, a temperature of the transducing head itself, or a part thereof, may be significantly higher than the temperature within the magnetic data storage and retrieval system due to heat dissipation caused by electrical currents in the transducer.
The coefficient of thermal expansion (CTE) of materials used in forming the substrate is typically much smaller than the CTE of materials used in forming the metallic layers of the transducer. Due to the large CTE of the transducer's metallic layers, those layers tend to expand a greater amount in response to high temperatures than will the substrate. Thus, when the transducing head is subjected to high operating temperatures, the metallic layers tend to protrude closer to the magnetic disc than the substrate; thereby affecting the PTR of the transducer. This change in PTR caused by temperature is referred to as the thermal protrusion.
During operation of the magnetic data storage and retrieval system, the transducing head is positioned in close proximity to the magnetic media. The distance between the transducer and the media is preferably small enough to allow for writing to and reading from the magnetic media with a large areal density, and great enough to prevent contact between the magnetic media and the transducing head. Performance of the transducer depends primarily on this distance between the media and the transducing head. To keep the distance between the transducing head and the magnetic media constant, PTR should not change significantly with temperature. If thermal protrusion is large, then the spacing between the transducer and the media will change significantly with temperature, thereby requiring the low-temperature fly height be enough to accommodate the higher operating temperatures. On the other hand, if thermal protrusion is close to zero, the low-temperature fly height can be reduced.
As areal density of the magnetic media increases, the requirements for transducing head fly height become such that thermal protrusion takes up a significant portion of the head disc spacing. The mismatched CTE between the materials of the transducing head, in particular the transducer, and the material of the substrate give rise to thermal protrusion. One method to reduce thermal protrusion is to introduce materials forming the transducer and/or materials near the transducer that have low coefficients of thermal expansion (GTE) to reduce or constrain the expansion of the transducer metals. However, constraining layers increases the stresses on the transducer structure and may also increase waviness of the ABS. Another method to reduce the thermal protrusion effect includes changing the reference surface for the air bearing surface to a material that expands and contracts with the transducer materials. However, changing reference surfaces is complex and may have negative impacts on other aspects of the disc drive system.
The present invention is a transducing head structure that reduces thermal protrusion when the transducing head is operated at high temperatures, but does not increase waviness of the ABS, have a negative impact on other aspects of the disc drive system, or over constrain the materials of the transducing head.